Low back pain is one of the most common reasons for people to seek care from a massage therapist. Unfortunately, despite all our advances in knowledge, most health care researchers admit that we still don't know what causes many cases of back pain. There are numerous suspected causes and biomechanical dysfunction in the lumbopelvic region is a frequent culprit. One biomechanical factor that causes low back pain is a leg length discrepancy (LLD).

Several months ago, a discussion of bodywork began on Yahoo! Groups about the role of pelvic rotation and LLD. This discussion eventually carried me into debates and conversations with a number of experts across multiple disciplines about the role of LLD and lumbopelvic pain. Thus, my perspective was significantly changed about how to assess LLD and the role it plays in various soft-tissue disorders.

There are two types of LLD, structural and functional. It is important to distinguish between the two as they are treated differently. A structural LLD also is called a true leg length discrepancy and is considered a true or structural discrepancy because the cause is an actual length difference in the lower extremity bones (femur or tibia). Also, structural LLD usually is congenital. Small discrepancies between the length of bones on each side of the body are common, but the problem occurs when the difference in length is more pronounced (usually .5 to 1 inch difference is considered within normal limits).1 Surgeries, accidents or previous fractures are other causes that produce a structural LLD.

Structural LLDs are treated with a heel lift if they are not severe; severe cases can require surgery. Before getting a heel lift, it is important to determine that there is a true structural discrepancy and not a functional one. The most accurate way to identify a structural LLD is with a lower extremity X-ray that allows a comparison of bone measurement with the other side. If X-ray evaluation is not an option, a comparison of the measurement between bony landmarks on each side with a tape measure is another option, although it is somewhat less accurate. Visual evaluation, such as that pictured in Figure 2, is commonly used to evaluate LLDs, but is the least accurate.

A functional LLD is more common than the structural-discrepancy type, however its cause can be hard to determine. Functional LLDs occur when it appears that one leg may be longer than the other, but there is no significant difference in the length of the lower extremity bones. Instead, a postural distortion has caused one lower extremity to appear longer or shorter than the other.

Figure 1 shows an example of how a functional LLD occurs from tight lumbar muscles. This is a posterior view of our client. The client has a tight left quadratus lumborum muscle that has pulled the left iliac crest in a superior direction. When you evaluate the height of each iliac crest in a standing position it appears that the left side is higher. If this client were supine, it would appear that the left leg is shorter because the pelvis and lower extremity on the left side are being pulled in a superior direction by the tight quadratus lumborum.

Some functional LLDs are harder to evaluate than others. A number of clinicians suggest that an anterior innominate rotation can produce an LLD. The innominate is one half of the pelvis and includes the ilium, ischium and pubis on one side. Each innominate can rotate independently of the other. Therefore, you can have one innominate that is anteriorly rotated and one that is more posteriorly rotated. If the client is supine, the anteriorly rotated innominate may appear to push the femur in a distal direction. When you evaluate the two legs using a method such as a visual leg length comparison (Figure 2), the leg on the side of the anteriorly rotated innominate could appear longer.

The problem with this evaluation method occurs when the person stands up. When the individual places weight on the lower extremity it affects innominate rotation. The innominate rotation can't push the femur inferiorly when the person is standing because the lower extremity is bearing weight (you would have to push the lower extremity into the ground). So what happens to the innominate rotation? Some people say it stays as an anterior rotation and others say weight bearing causes a reverse (posterior) rotation of the innominate. However, there is very little biomechanical research on this issue to clarify what actually occurs.

Bearing weight does not change a functional LLD that is caused by a tight quadratus lumborum (Figure 1). When the individual stands upright, the pelvis still will appear high on the side of the apparent short leg. This apparent LLD remains because it is caused by the innominate on that side being pulled superiorly and not because a lower extremity is being pushed down in an inferior direction.

After consulting numerous resources and conversing with experts on this issue, it is clear that there is no consensus on what happens with functional LLDs caused by innominate rotation when the individual is weight bearing. Yet there is agreement that most functional LLDs that cause back pain are created by soft-tissue dysfunction and can be corrected by manual methods such as massage. Several good recommendations are provided in Erik Dalton's article on the "Short Leg Syndrome" in the November 2007 issue of
Massage Today.

LLD, whether structural or functional, is an important contributor to lumbopelvic pain. What is still not clear is exactly how the mechanics of the sacroiliac joint, lumbar spine and hip directly cause specific pathological problems with an LLD. If there is a simple mechanical cause of pain there should be a strong correlation between the assessment of LLD and specific symptoms of lumbopelvic pain. Unfortunately, there is a poor relationship between evaluation methods for pelvic position and specific pain complaints.2,3 Additional research is highly needed to help us understand the complex biomechanics of this region and exactly what role innominate position or leg length play in lumbopelvic pain.

References

1. Magee D. Orthopedic Physical Assessment. 3^rd ed. Philadelphia: W.B. Saunders, 1997.
2. Schneider M, Homonai R, Moreland B, Delitto A. Interexaminer reliability of the prone leg length analysis procedure. J Manipulative Physiol Ther, September 2007;30(7):514-21.
3. Vleeming A, Mooney V, Dorman T, Snijders C, Stoeckart R. Movement, Stability, & Low Back Pain. New York: Churchill Livingstone, 1999.